When the data contains a property conflicting with the reserved QgsField name, e.g. 'FID' conflicts with 'fid' used internally in gpkg file. Since the column names are case-insensitive in Geopackage file, it may cause problems with the loaded data, for instance:
When the data contains a property conflicting with the reserved QgsField name, e.g. 'FID' conflicts with 'fid' used internally in gpkg file. Since the column names are case-insensitive in Geopackage file, it may cause problems with the loaded data, for instance: